Add month number column from timestamp column

I have a time column, with timestamps in the form 2018-04-12 06:48:39. How can I add a column Month from this timestamp, in this case containing 4?

pyspark.sql.functions.month:

import pyspark.sql.functions as F
df.withColumn('month', F.month('time')).show()
+-------------------+-----+
|               time|month|
+-------------------+-----+
|2018-04-12 06:48:39|    4|
+-------------------+-----+